1. Field of the Invention
The invention generally relates to a back light module and a display apparatus, and more particularly, to a edge-type back light module and a liquid crystal display (LCD).
2. Description of Related Art
The LCD has played a major role in the mainstream display apparatus market in recent years due to advantages of low voltage operation, no radiation, light and compact design. An LCD mainly includes a liquid crystal panel and a back light module, wherein the back light module is for providing a planar light source required by the liquid crystal panel so as to make the LCD displaying. The LCD controls the rotations of the liquid crystal molecules in the liquid crystal panel so as to determine the light flux for producing gray level variations and thereby constituting a static or dynamic image.
When human-eyes watch dynamic images played on an LCD, every digital frame would stay for a while and then to be updated to the next frame. Therefore, in successive frames of digital images, a moving object is not displayed in continuous moving way, but in step moving way. When human-eyes are watching a moving object, the positions of the object moving would be traced by the human-eyes. In particular, during switching the frames of the LCD, the back light module still keep providing the light. As a result, the human-eyes easily have noticed that the object moves not continuously during switching the frames (i.e., during the rotations of the liquid crystal molecules). Since the positions of the images of a same moving object come from the successive frames staying on the retinas are different, the double image phenomena are presented, which leads to blurry image profiles and further gives the display quality of the LCD a negative impact.
In order to solve the above-mentioned problem, a scan-type back light module was provided, where a regional lighting method is adopted so as to reduce the chance for human-eyes to see frame switching blur. In a direct-type back light module, the light-emitting devices of each region are turned on alternately one after another so as to more easily achieve the objective of regional lighting. However, the direct-type back light module has a disadvantage of larger overall thickness. A edge-type back light module, in order to achieve the same objective of regional lighting, employs a plurality of light-emitting devices respectively arranged in each region and adopts the regional lighting method. At each region, a corresponding independent sub-light-guide-plate (sub-LGP) is disposed, and all the sub-LGPs are assembled together. Although the edge-type back light module is advantageous in smaller overall thickness, but the plurality of sub-LGPs are not easy to be well aligned, which is resulted in poor optical quality. In addition, with a edge-type back light module, since each independent sub-LGP has a manufacturing tolerance, the length, the width and the thickness thereof have inconsistency from each other, hence after assembling, the optical quality of each region is uneven from the other regions, and bright lines likely appear at the seams between the independent sub-LGPs.